Antennas with ultra-wide bandwidth have usually been too large to consider for arrays. Examples are spirals and log-periodic slots. They are also often inefficient because they are backed with absorber-filled cavities. The absorber attenuates the received RF power by one-half. Still other ultra-wideband antennas such as flared notches are very deep, resulting in unacceptable intrusion into, or protrusion from the supporting structure. On the other hand, antennas that are compact and amendable to conformal flush-mounting, are usually very narrowband. Examples are cavity-backed slots and microstrip patches. Their bandwidths are typically limited to less than 10%, or 1.1:1. Furthermore, their bandwidth decreases when they are used in arrays.